Dry etching method

ABSTRACT

The present invention is concerned with a dry-etching method wherein a gaseous mixture of boron trichloride, chlorine and a hydrocarbon, to be used as an etching gas, is converted into plasma to etch aluminum or its alloys with ions or radicals formed thereby. The invention makes it possible to accomplish the anisotropic etching of aluminum or its alloys at high speeds with a low RF power density.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dry etching method, and particularlyto a dry etching method for accurate anisotropic etching of aluminum orits alloys at high speeds.

2. Description of the Prior Art

Aluminum or its alloys that form electrodes and wirings of semiconductorintegrated circuits are dry-etched by using, as an etching gas, agaseous mixture of boron trichloride (hereinafter referred to as BCl₃),chlorine (hereinafter referred to as Cl₂), methyl trichloride(hereinafter referred to as CHCl₃) and helium (hereinafter referred toas He) as disclosed in, for example, R. H. Bruce et al., J. Electrochem.Soc., Vol. 130, No. 6, pp. 1369-1372 (1983.6), or by using a gaseousmixture of BCl₃, Cl₂, silicon tetrachloride (hereinafter referred to asSiCl₄) and He as disclosed in R. F. Reicheldefer, Solid StateTechnology, Vol. 15, No. 6, pp. 64-75 (1982.6)

When aluminum or its alloys are dry-etched using, as an etching gas, thegaseous mixture of BCl₃, Cl₂, CHCl₃ and He, or that of BCl₃, Cl₂, SiCl₄and He, the etching can be accomplished at a high speed andanisotropically free from undercutting. To accomplish the anisotropicetching at a high speed, however, the RF power density (RF power dividedby electrode area, the unit being in W/cm²) must be maintained at ashigh as, for instance, 1.8 W/cm₂ when the mixture of BCl₃, Cl₂, CHCl₃and He is used as an etching gas, or 2.2 to 3 W/cm2 when the mixture ofBCl₃, Cl₂, SiCl₄ and He is used as an etching gas. Therefore, whenanisotropically etching aluminum or its alloys at high speeds using, asan etching gas, the gaseous mixture of BCl₃, Cl₂, CHCl₃ and He, or thatof BCl₃, Cl₂, SiCl₄ and He, the capacity of the RF power source must beincreased, and photoresist applied onto the surface of a semiconductorsubstrate to be etched, is liable to be damaged and thus an anisotropicetching with a small line-width loss, i.e., an accurate anisotropicetching, will not be readily accomplished.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a dry etching methodwhich makes it possible to accomplish a high speed and accurateanisotropic etching of aluminum or its alloys.

According to the present invention, a gaseous mixture of BCl₃, Cl₂ andhydrocarbon, where the ratio of the content of the Cl₂ to the sum of thecontents of the BCl₃ and Cl₂ is 40 to 80% by volume and the ratio of thecontent of the hydrocarbon to be added to the sum of the contents of theBCl₃ and Cl₂ is 5 to 30% by volume, is used as an etching gas, and theetching gas is converted into plasma to etch aluminum or its alloys withplasma and thereby the present invention makes it possible to accomplisha high speed and accurate anisotropic etching of aluminum and itsalloys. Namely, according to the present invention, aluminum or itsalloys can be anisotropically etched at high speeds with a low RF powerdensity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 pertains to the anisotropy of etching for aluminum according tothe method of the present invention and shows a relationship between theratio of addition of methane as a hydrocarbon to the gaseous mixture ofBCl₃ and Cl₂ and the line-width loss (=width of photoresist before theetching - width of aluminum pattern after the etching), and

FIG. 2 pertains to the high speed characteristics of aluminum etchingand shows a relationship between the ratio of methane addition and theetching speed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Aluminum, Al-Si alloy, and Al-Si-Cu alloy were etched while varying theflow rate of hydrocarbon gas added to the gaseous mixture of BCl₃ andCl₂ under the conditions of a RF power density of 0.7 to 1.5 W/cm² and aratio of Cl₂ flow rate to the resultant flow rate of BCl₃ and Cl₂(hereinafter referred to as Cl₂ ratio) of 40 to 80% by volume. Asemiconductor substrate of which the surface to be etched had beenpatterned with a photoresist was placed on one of a pair of electrodesdisposed in an evacuated processing chamber and a RF power of 13.56 MHzwas applied to the electrode on which the substrate had been placed. Theresults obtained were as shown in FIGS. 1 and 2, wherein thesemiconductor substrate was composed of aluminum, the RF power densitywas 1.0 W/cm², and the Cl₂ ratio was 50% by volume (the resultant flowrate of BCl₃ and Cl₂ being 80 SCCM). Methane (hereinafter referred to asCH₄) was used as a hydrocarbon gas.

When no CH₄ is added in FIG. 1, i.e., when only a gaseous mixture ofBCl₃ and Cl₂ is used, the dimension of wiring is narrowed due to thedevelopment of undercutting; i.e., the line-width loss amounts to asgreat as 0.5 μm to reduce the accurate anisotropy. On the other hand,the development of undercutting is decreased and the line-width loss isreduced, as the CH₄ gas is added at an increased flow rate to themixture of BCl₃ and Cl₂, i.e., as the ratio of the CH₄ gas flow rate tothe amount of the gaseous mixture of BCl₃ and Cl₂ (hereinafter referredto as the ratio of CH₄ addition) increases. The line-width loss becomesminimal, i.e., 0.1 μm, and the accurate anisotropy is sufficientlyaccomplished when the flow rate of CH₄ gas is about 10 SCCM, i.e., whenthe accurate ratio of CH₄ addition is about 13% by volume. If the flowrate of CH₄ gas is further increased, i.e., if the ratio of CH₄ additionis further increased, the line-width loss rather increases due to theregression of the photoresist though the accurate anisotropy of etchingis still maintained. Thus, the line-width loss amounts to about 0.3 μmwhen the flow rate of CH₄ gas is 40 SCCM, i.e., when the ratio of CH₄addition is 50% by volume.

In FIG. 2, the etching speed is as high as about 1800 nm/min when no CH₄is added, i.e., when the mixture consisting of only BCl₃ and Cl₂ isused. On the other hand, the etching speed decreases as the flow rate ofCH₄ gas increases, i.e., as the ratio of CH₄ addition increases. Forinstance, the etching speed is about 1200 nm/min when the flow rate ofCH₄ gas is 10 SCCM, i.e., when the ratio of CH₄ addition is about 13% byvolume, about 200 nm/min when the flow rate of CH₄ gas is 20 SCCM, i.e.,when the ratio of CH₄ addition is 25% by volume, and about 20 nm/minwhen the flow rate of CH₄ gas is 40 SCCM, i.e., when the ratio of CH₄addition is 50% by volume.

As shown in FIGS. 1 and 2, the line-width loss can be suppressed to 0.1μm and the etching speed can be increased to about 1200 nm/min to effectthe anisotropic etching at a high speed with a RF power density of aslow as 1.0 W/cm² when the flow rate of CH₄ gas is set at about 10 SCCM,i.e., when the ratio of CH₄ addition is set at 13% by volume.

To accomplish the anisotropic etching of aluminum or its alloys at highspeeds under the conditions of a RF power density of 0.7 to 1.5 W/cm²and a Cl₂ ratio of 40 to 80% by volume, the ratio of CH₄ addition mustbe properly selected depending upon the pressure in the processingchamber during etching and the distance between the electrodes. Forexample, when the pressure in the processing chamber is 20 to 60 Pa andthe distance between the electrodes is 20 to 50 mm, the ratio of CH₄addition should be selected to lie within a range of 5 to 30% by volume.

According to this embodiment, the etching of aluminum and its alloys canbe accomplished with such a low RF power density as 0.7 to 1.5 W/cm² anddamage to the photoresist can be restrained and, therefore, at a highspeed an accurate anisotropic etching of aluminum and its alloys can beaccomplished and the capacity of the RF power source can also bereduced.

In this embodiment, also, CH₄ is used as a hydrocarbon that is to beadded to the gaseous mixture of BCl₃ and Cl₂. However, the same effectscan also be obtained even when C₂ H₆, C₃ H₈, C₂ H₂, C₂ H₄, or C₃ H₄ isused. The above-described embodiment has been described with referenceto an etching apparatus where a processing chamber with a pair ofelectrodes and a RF power is applied to one of the electrodes on which asample is to be placed. It will be appreciated that such effects asdescribed in this embodiment will be accomplished by other type ofplasma etching apparatus.

According to the present invention as described above, a gaseous mixtureof BCl₃, Cl₂ and hydrocarbon, to be used as an etching gas, is convertedinto plasma to etch aluminum or its alloys with ions or radicals formedthereby. Therefore, aluminum or its alloys can be anisotropically etchedat high speeds with a low RF power density.

What is claimed is:
 1. A dry etching method wherein a gaseous mixture ofboron trichloride, chlorine and hydrocarbon, where the ratio of thecontent of the chlorine to the sum of the contents of the borontrichloride and the chlorine is 40 to 80% by volume and the ratio of thecontent of the hydrocarbon to the sum of the contents of borontrichloride and chlorine is 5 to 30% by volume, is used as an etchinggas, and said etching gas is converted into plasma to etch aluminum orits alloys with said plasma.
 2. A dry etching method according to claim1, wherein methane is used as said hydrocarbon.